In the present study, a mechanism of zigzagging bubble motion was experimentally and quantitatively investigated. We focused on a relationship between the bubble motion (gravity-center motion and surface motion) and its surrounding liquid motion. We visualized the bubble motion and its surrounding liquid motion simultaneously using IST (Infrared Shadow Technique) and SPIV (Stereo Particle Image Velocimetry). The interrogation areas were located just above a needle (just after bubble launch) to the first inversion of the zigzagging trajectory (transition from the linear to the zigzag). First, the bubble trajectory, the surface motion and the bubble inclination angle of major axis were obtained from the IST images. Second, the pseudo-3D motions (2D-3C velocity fields) of the surrounding liquid were calculated from the SPIV results. Based on the velocity data, we calculated the surrounding pressure field around the bubble by solving simplified Navier-Stokes Equation. Finally, from these results, we quantitatively discuss the close relationship between the bubble motion and its surrounding liquid motion. In particular, we discuss the mechanism of the zigzagging motion. At the inversion point, the shape deformation of the bubble and the fluctuation of the surrounding liquid motion show distinctive behavior. We tentatively consider that the zigzagging motion is caused by the periodical fluctuation of the bubble deformation (the surface motion and the inclination angle of major axis) and the surrounding liquid motion; i.e. the asymmetry of the surrounding liquid (velocity and pressure) induced by the bubble surface oscillation characterizes the zigzag motion.

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